Chemical reducing agents of enhanced hydrocarbon solubility

ABSTRACT

THE HYDROCARBON SOLUBILITY OF ALKALI METAL ALUMINUM DIALKYL DIHYDRIDES, CHEMICAL REDUCING AGENTS, IS ENHANCED BY INCLUDING IN THE SOLUTION A SMALL QUANTITY OF A SUITABLE INNOCUOUS LEWIS BASE.

United States Patent 3,696,047 CHEMICAL REDUCING AGENTS OF ENHANCED HYDROCARBON SOLUBILITY Gunner E. Nelson, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y. No Drawing. Filed Oct. 15, 1970, Ser. No. 81,164 Int. Cl. C09k 3/00 U.S. Cl. 252-188 23 Claims ABSTRACT OF THE DISCLOSURE The hydrocarbon solubility of alkali metal aluminum dialkyl dihydrides, chemical reducing agents, is enhanced by including in the solution a small quantity of a suitable innocuous Lewis base.

Alkali metal aluminum dialkyl dihydrides have been suggested for use as reducing agents (Ziegler et al. US. 2,915,541; 3,143,542). Unfortunately, however, the hydrocarbon solubility of these compounds, especially the sodium aluminum dialkyl dihydrides, is not as high as one might wish. For example, high purity sodium aluminum diethyl dihydride is virtually insoluble in parafiinic hydrocarbons although it is soluble to some extent in aromatic hydrocarbons. In my prior copending application Ser. No. 79,682 (Case 3558, executed by me on Oct. 8, 1970), filed Oct. 9, 1970 and entitled Chemical Reducing Agent it has been pointed out that sodium aluminum diethyl dihydride is more soluble and more stable in liquid alkyl benzenes than it is in benzene.

Despite the higher solubility of sodium aluminum diethyl dihydride in alkyl benzenes it would be of particular advantage to be able to increase the solubility of alkali metal aluminum dialkyl dihydrides in all types of hydrocarbon solvents.

In accordance with this invention the hydrocarbon solubility of alkali metal aluminum dialkyl dihydrides is increased by including in the solution a small quantity of an innocuous hydrocarbon-soluble Lewis base such as tertiary amine, an ether, or the like. The presence in the system of the small quantity of Lewis base significantly increases the solubility of the alkali metal aluminum dialkyl dihydride in all types of hydrocarbon solventsi.e., parafiins, cycloparafiins, and aromatics. Accordingly, this invention enables the provision of more concentrated reagent solutions of the alkali metal aluminum dialkyl dihydrides. Under normal conditions, the solutions may be stored, transported and used without incurring phase separatione.g., formation of sediments or precipitates. Further, excessive shipping costs for the reducing agent solutions may be avoided. In handling the reagent solutions, ordinary precautions should be observed such as avoiding exposure to flames or excessive exposure to moisture or the atmosphere.

'One embodiment of this invention provides a process of increasing the solubility of an alkali metal aluminum dialkyl dihydride in a hydrocarbon solvent which comprises including in the solution a small quantity of an innocuous hydrocarbon-soluble Lewis base.

In another embodiment this invention provides a liquid hydrocarbon having dissolved therein an alkali metal aluminum dialkyl dihydride and a small amount of an innocuous hydrocarbon-soluble Lewis base. Other embodiments will become readily apparent to one skilled in the art upon a consideration of the ensuing disclosure and appended claims.

The alkali metal aluminum dialkyl dihydrides involved in the present invention include those in which the alkali metal constituent is lithium, sodium, potassium, rubidium, or cesium. However, the invention is most preferably applied to the sodium aluminum dialkyl dihydrides, especially those having up to about 4 carbon atoms in each alkyl group as these compounds are among the most effective reducing agents of the class and can be prepared from relatively inexpensive and readily available raw materials.

Exemplary alkali metal aluminum dialkyl dihydrides to which this invention may be applied include lithium aluminum dimethyl dihydride, lithium aluminum diethyl d hydride, lithium aluminum dibutyl dihydride, sodium aluminum dipentyl dihydride, sodium aluminum dihexyl dihydride, sodium aluminum dioctyl dihydride, potassium aluminum diethyl dihydride, potassium aluminum diisobutyl dihydride, potassium aluminum dihexyl dihydride, rubidium aluminum didodecyl dihydride, cesium aluminum dioctadecyl dihydride, and the like. Among the preferred sodium compounds are sodium aluminum dimethyl dihydride, sodium aluminum diethyl dihydride, sodium aluminum dipropyl dihydride, sodium aluminum dibutyl dihydride and sodium aluminum diisobutyl dihydride.

A few illustrative hydrocarbons which may be used as solvents in the practice of this invention include the paraffinic hydrocarbons such as pentane, hexane, octane, dodecane and petroleum ether; cycloparaffinic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexanes, cycloheptane, cyclooctane, and decahydronaphthalene; and aromatic hydrocarbons such as benzene, toluene, the xylenes, mesitylene, the cymenes, cumene, the ethyl toluenes, the diethyl benzenes, butyl 'benzene, sec-butyl benzene, tort-butyl benzene, tetrahydronaphthalene and the like. These solvents should have freezing points below about 15 C. and more preferably below 0 C.i.e., they should exist in the liquid state of aggregation under average room temperature conditions. The preferred solvents are alkyl benzenes as these confer enhanced stability to the system. The use of toluene or xylene (the ortho, meta, or para isomers; or mixed isomers) is particularly preferred as the resultant solutions have good thermal stability and handling properties, and the solvents are relatively inexpensive and readily available.

The solubility of alkali metal aluminum dialkyl dihydrides in hydrocarbons will vary depending upon such factors as the identity of the alkali metal aluminum dialkyl dihydride, the identity of the hydrocarbon solvent and the temperature of the system. A feature of this invention is that even where the solubility of the alkali metal aluminum dialkyl dihydride in a given hydrocarbon is substantial under a given set of conditions, the inclusion in the the system of a small quantity of an innocuous hydrocarbon-soluble Lewis base will improve the solubility so that under a different set of conditions (e.g., reduction in temperature) there will be a reduced tendency for separation of the alkali metal aluminum dialkyl dihydride to occur. The invention is most preferably applied however to systems wherein the solubility of the alkali metal aluminum dialkyl dihydride in the hydrocarbon at 25 C. does not exceed about 30 weight percent in the absence of the Lewis base component.

A wide variety of Lewis bases are available for use in practicing this invention. The only requirements are that the Lewis base be hydrocarbon-soluble and that it be innocuous in the sense that it may form a soluble complex with the alkali metal aluminum dialkyl dihydride and it may dissociate associated molecules of the alkali metal aluminum dialkyl dihydride but it otherwise is non-reactive therewith. It is postulated that the Lewis base may function toincrease the hydrocarbon solubility of alkali metal aluminum dialkyl dihydrides by causing dissociation or breakdown of associated molecules of the alkali metal aluminum dialkyl dihydride. It is thought that high purity alkali metal aluminum dialkyl dihydrides normally tend to form intermolecular complexes (perhaps through hydrogen bonding) with the result that the higher molecular weight complex has a lower hydrocarbon solubility than the unpolymerized or the non-associated species. In accordance with this hypothesis it is further envisioned that the Lewis base may not only dissociate the polymerized molecules but may complex with the dissociated molecules to yield complexes of enhanced hydrocarbon solubility. It will of course be understood and appreciated by those skilled in the art that this invention is in no way limited or restricted to the foregoing or to any other explanation as to the theoretical mechanisms by which the improved hydrocarbon solubility is achieved. Whatever the explanation and by whatever means the desirable result is actually brought about, the invention requires only the incorporation in the system of a small amount of an innocuous hydrocarbon-soluble Lewis base to achieve the desired result. Accordingly, the innocuous Lewis bases which are used in the practice of this invention are compounds which contain no functionality that would adversely react with the alkali metal aluminum dialkyl dihydride at temperatures under which the hydride will be put to its intended use. For example, the Lewis base will not contain reducible non-aromatic unsaturated nor such reducible functional groups as hydroxyl, sulfhydryl, carbonyl, carboxyl, peroxy, or like groups.

Generally speaking, Lewis bases which are suitable for the practice of this invention include ethers, tertiary amines, tertiary phosphines, tertiary arsines, tertiary stibines, and other organic Lewis bases having the character and attributes referred to above. From the cost elfectiveness standpoint the use of tertiary amines and ethers is preferred.

Exemplary Lewis bases include tertiary hydrocarbyl amines (aliphatic, aromatic, or heterocyclic) such as trimethyl amine, triethyl amine, tributyl amine, N,N-dimethyl aniline, pyridine, N-methyl piperidine, N,N,N',N'- tetramethylethylenediamine, triethylene diamine, N,N-diethyltoluidine, N,N-dimethyl piperazine, triphenyl amine, and other tertiary amine bases found in any appropriate text book of organic chemistry; and hydrocarbyl ethers such as diethyl ether, dibutyl ether, the dimethyl ether of ethylene glycol, the diethyl ether of ethylene glycol, trimethylol propane, the dimethyl ether of diethylene glycol, the diethyl ether of diethylene glycol, the dibutyl ether of diethylene glycol, the dimethyl ether of tetramethylene glycol, 1,3-dioxolane, 1,4-dioxane, tetrahydropyran, diphenyl ether, and other cyclic or acyclic mono or poly ethers referred to in the literature including, for example, the crown compounds discussed in J. Am. Chem. Soc., 89, 7017 (1967). Of the ethers, the cyclic monoethers such as tetrahydrofuran and alkyl substituted tetrahydrofurans are particularly convenient, effective and relatively inexpensive, and thus their use constitutes a preferred embodiment of this invention.

Exemplary tertiary hydrocarbyl phosphines include triethyl phosphine, tributyl phosphine, triphenyl phosphine, tricyclohexyl phosphine, and other analogous compounds. The corresponding trihydrocarbyl derivatives of arsenic and antimony are also suitable as are other innocuous hydrocarbon-soluble Lewis bases. The suitability of any given Lewis base for use in the practice of this invention can be readily ascertained by the simple expedient of performing a few laboratory tests. Given the teachings of this invention one skilled in the art should have no difficulty in finding numerous and sundry suitable Lewis bases whether or not they are specifically referred to herein.

Although the proportions of the Lewis base may be varied to suit the needs of the occasion the solution of the alkali metal aluminum dialkyl dihydride in a hydrocarbon solvent will usually contain from about 0.5 to about percent, and preferably from about 0.5 to about 5 percent, by weight of the Lewis base. When using the ethers, especially tetrahydrofuran and hydrocarbonsoluble derivatives thereof, concentrations in the finished solution ranging from about 0.5 to about 1.5 percent by weight based on the total weight of solution are found especially advantageous.

The following examples are illustrative of this invention and its advantages.

EXAMPLE I Sodium aluminum diisobuty] dihydride normally has a solubility in toluene at room temperature of about 5 to 6 percent by weight. However incorporation in the solution of 5 percent of tetrahydrofiuran based on the total weight of the solution increases the solubility so that the solution may contain as much as 22 percent by weight of sodium aluminum diisobutyl dihydride.

EXAMPLE II Under room temperature conditions sodium aluminum diethyl dihydride is sufiiciently soluble in toluene to furnish solutions containing somewhat above 16 weight percent of the reagent. However, when tetrahydrofuran is included in the solution at a concentration of 1.1 percent by weight based on the total weight of the solution the solubility of the sodium aluminum diethyl dihydride is increased to the extent that the solution may contain at least as much as about 28 percent by weight.

EXAMPLE HI At 25 C. the solubility of sodium aluminum diethyl dihydride in mixed xylene isomers enables the preparation of solutions containing approximately 26 weight percent of the hydride. However when the solution also contains tetrahydrofuran (one percent based on the total weight of the solution) it is possible to provide solutions containing at least as much as 41 percent by weight of the sodium aluminum diethyl dihydride.

I claim:

1. A process of increasing the solubility of an alkali metal aluminum dialkyl dihydride in a hydrocarbon solvent which comprises including in the solution a small quantity in the range of from about 0.5 to about 10 percent by weight of an innocuous hydrocarbon-soluble organic Lewis base, innocuous in the sense that it may form a soluble complex with the alkali metal aluminum dialkyl dihydride and it may dissociate associated molecules of the alkali metal aluminum dialkyl dihydride but it otherwise is non-reactive therewith.

2. The process of claim 1 wherein the Lewis base is a tertiary amine.

th3. The process of claim 1 wherein the Lewis base is an e er.

4. The process of claim 1 wherein the Lewis base is a cyclic monoether.

5. The process of claim 1 wherein the hydrocarbon solvent is a liquid alkyl benzene.

6. The process of claim 1 wherein the hydrocarbon solvent is toluene or xylene.

7. The process of claim 1 wherein the alkali metal aluminum dialkyl dihydride is a sodium aluminum dialkyl dihydride.

8. The process of claim 1 wherein the hydrocarbon solvent is a liquid mononuclear aromatic hydrocarbon, wherein the alkali metal aluminum dialkyl dihydride is a sodium aluminum dialkyl dihydride, and wherein the Lewis base is a tertiary amine.

9. The process of claim 1 wherein the hydrocarbon solvent is a liquid mononuclear aromatic hydrocarbon, wherein the alkali metal aluminum dialkyl dihydride is a sodium aluminum dialkyl dihydride, and wherein the Lewis base is a monoether.

10. The process of claim 1 wherein the hydrocarbon solvent is toluene or xylene, wherein the alkali metal aluminum dialkyl dihydride is sodium aluminum diethyl dihydride, and wherein the Lewis base is tetrahydrofuran or alkyl substituted tetrahydrofuran.

11. A liquid hydrocarbon having dissolved therein an alkali metal aluminum dialkyl dihydride and a small amount in the range of from about 0.5 to about percent by weight of an innocuous hydrocarbon-soluble organic Lewis base, innocuous in the sense that it may form a soluble complex with the alkali metal aluminum dialkyl dihydride and it may dissociate associated molecules of the alkali metal aluminum dialkyl dihydride but it otherwise is non-reactive therewith.

12. The composition of claim 11 wherein the hydrocarbon is a liquid aromatic hydrocarbon, wherein the alkali metal aluminum dialkyl dihydride is a sodium aluminum dialkyl dihydride having up to about 4 carbon atoms in each alkyl group and wherein the Lewis base is an ether.

13. The composition of claim 11 wherein the hydrocarbon is a liquid aromatic hydrocarbon, wherein the alkali metal aluminum dialkyl dihydride is a sodium aluminum dialkyl dihydride having up to about 4 carbon atoms in each alkyl group and wherein the Lewis base is a cyclic monoether.

14. The composition of claim 11 wherein the hydrocarbon is toluene or xylene, wherein the alkali metal aluminum dialkyl dihydride is sodium aluminum diethyl dihydride and wherein the Lewis base is tetrahydrofuran present in an amount of from about 0.5 to about 5 percent by weight based on the total weight of the solution.

15. The composition of claim 11 wherein the hydrocarbon is a mixture of xylene isomers, wherein the alkali metal aluminum dialkyl dihydride is sodium aluminum diethyl dihydride and wherein the Lewis base is tetrahydrofuran present in an amount of from about 0.5 to about 1.5 percent by weight based on the total weight of the solution, the sodium aluminum diethyl dihydride being present in an amount of at least about 25 percent by weight based on the total weight of the solution.

16. The composition of claim 11 wherein the hydrocarbon is toluene, wherein the alkali metal aluminum dialkyl dihydride is sodium aluminum diethyl dihydride and wherein the Lewis base is tetrahydrofuran present in an amount of from about 0.5 to about 1.5 percent by weight based on the total weight of the solution, the sodium aluminum diethyl dihydride being present in an amount of at least about 15 percent by weight based on the total weight of the solution.

17. The process of claim 1 wherein said Lewis base is selected from the group consisting of ethers, tertiary amines tertiary phosphines, tertiary arsines, and tertiary stibines.

18. The process of claim 1 wherein the hydrocarbon solvent is a liquid mononuclear aromatic hydrocarbon, wherein the alkali metal aluminum dialkyl dihydride is a sodium aluminum dialkyl dihydride in which each alkyl group contains from 1 to 4 carbon atoms and wherein said Lewis base is an ether employed in an amount ranging from about 0.5 to about 5 perecnt by weight of the solution.

19. The process of claim 1 wherein the solubility of the alkali metal aluminum dialkyl dihydride in the hydrocarbon at 25 C. does not exceed about 30 weight percent in the absence of said Lewis base.

20. The process of claim 1 wherein the Lewis base is an ether employed in an amount ranging from about 0.5 to about 1.5 percent by weight based on the total weight of the solution.

21. The composition of claim 11 wherein the solubility of the alkali metal aluminum dialkyl dihydride in the hydrocarbon at 25 C. does not exceed about 30 weight percent in the absence of said Lewis base.

22. The composition of claim 11 wherein said Lewis base is an ether present in an amount ranging from about 0.5 to about 5 percent by weight based on the total weight of the solution.

23. The composition of claim 11 wherein said Lewis base is tetrahydrofuran or alkyl substituted tetrahydrofuran present in an amount ranging from about 0.5 to about 5 percent by weight based on the total weight of the solution.

References Cited Coates et al., Organo Metallic Compounds, Vol. 1, 3rd Ed. (1967), Butler et a1. Pub. pp. 30415.

Nesmeyanov et al., Methods of Elements-Organic Chemistry, Vol. I (1967) pp. 497-9, North Holland.

Zeiss, Organo Metallic Chemistry .(1960) pp. 211-12, Reinhold.

JOHN D. WELSH, Primary Examiner U .5. Cl. X.R. 260448 

